userv-ipif: Always request routes from userv, regardless of link quality

Previously the userv-ipif netlink would not request (from userv) a
route for a site for which the link quality was DOWN.  The link
quality is a dynamic quantity but userv-ipif lacks any machinery for
dynamically adding routes, so this is wrong.

Instead, in userv-ipif, unconditionally add routes for all sites,
regardless of link up status.

In practice this code is run during startup and the only reason a link
might be down at that point, ie LINK_QUALITY_DOWN, is that it does not
have an address configured.  Mobile sites are often in this situation.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>